1. Field of the Invention
The invention relates generally to the design of lubricator valves used for installing tools in a live oil or gas well on wireline while controlling fluids therethrough.
2. Description of the Related Art
During operation of live oil or gas wells, it is sometimes necessary to run a tool, such as a perforating gun, into the well. Because the well is live, it may be under pressure and, therefore, it is necessary to use a device known as a lubricator valve to allow passage of the tool while controlling the flow of pressurized fluid. Sometimes the lubricator valve is located at the surface, above the wellhead. A surface-based lubricator valve is a pressure-retaining container that is used to hold the wireline tool string before it gets deployed downhole. It is often necessary, however, to locate the lubricator valve below the surface of the well. The need to deploy longer logging tools or perforating guns, for example, is a limitation for surface lubricators due to the required height of the lubricator chamber. Applicable safety requirements specify that downhole wireline running arrangements have a minimum of two safety valves (ball or flapper type) to hold the live well pressure. The upper safety valve is closed to pressure test the wellhead pressure from above. The lower safety valve is used to hold pressure from below. The lubricator valve must facilitate pressure testing from both above and below.
Subsurface lubricator valves of various construction are known. U.S. Pat. No. 4,846,281, issued to Clary et al., for example, describes a dual flapper valve apparatus that is used for protecting a well during a gravel packing operation. One problem with this type of arrangement is that the flapper valves close against a valve seat that is located below the flapper valve member. As a result, the flappers open by pivoting upwardly from the closed position. In the event that there is debris atop either flapper member that has accumulated during the pressure testing process, the flapper member(s) may be difficult to open afterward. A further problem with conventional lubricator valves of this type is that the flapper-type safety valves rely solely upon a torsion spring to close the flapper element. If this torsion spring is damaged, the flapper valves within the lubricator valve will fail to close properly.
An additional problem with conventional lubricator valve designs is that there is no bi-directional sealing. When the flapper members are closed, there is no mechanism to secure the flappers in the closed position. Thus, pressure testing can only be accomplished from a single direction as pressurizing the valve in the opposite direction will open the flapper valves. Pressure testing in both directions is important for ensuring the safety of a lubricator valve.
The present invention addresses the problems of the prior art.